Hydrogen is an extremely clean energy source for use in fuel cells and internal combustion engines. However, widespread use of hydrogen as a fuel will require innovations in hydrogen storage and hydrogen sensing. Reliable, cheap, compact, and safe hydrogen sensors are needed both for measuring the hydrogen concentration in flowing gas streams and for monitoring ambient air for leaked hydrogen. It is essential that “alarm” sensors detect hydrogen at a concentration well below the lower explosion limit in air of 4%.
Currently, commercial hydrogen sensors suffer from their lengthy response time and high cost. In addition, the working temperatures are usually high. Therefore, explorations for new methods that lead to inexpensive, convenient and fast response hydrogen sensors are crucial for the future application of hydrogen fuel. Palladium metal has long been recognized as the desired material for hydrogen sensing. In principle, Pd metal swells upon exposure to hydrogen gas that results in resistance change. Recent advances in the synthesis of Pd nanostructure based hydrogen sensors lead to a series of new results. Prior art shows that Pd nanostructure based hydrogen sensors are promising due to a decrease in response time. In particular, Pd nanoparticle based hydrogen sensors respond to hydrogen gas in milliseconds. The difficulty is finding an appropriate carrier that can load palladium nano-particles and functions as a sensor.
Anodized aluminum oxide (AAO) membranes consist of highly uniform and aligned nanopores (hexagonal close packed) with the pore diameter ranging between 10 and 200 nanometers (nms). AAO nanowell structure can be synthesized through short-term anodization of aluminum metal. We found that the thin AAO nanowell structure is an excellent substrate for hydrogen sensing because not only does it provide a rough surface with large surface areas which is a perfect medium for supporting Pd nanostructures but also the surfaces are weakly conductive for better electronic measurements. AAO nanowell hydrogen sensors coated with Pd nanostructures can be achieved either by thermal evaporation or chemical coating Pd metal on an AAO nanowell surface.